1. Field of the Invention
The present invention relates to a method of making conductive elements and in particular, to making patterned conductive elements suitable for use in the manufacture of implantable medical devices.
2. Related Art
Medical devices that are implanted in the body are subject to a large range of design and manufacturing constraints.
Such medical devices need to be as small as possible to ensure they are minimally invasive. The order of size for components can be in the micron scale.
Further, the materials from which the devices are made must be “biocompatible”. This means they must have been proven to not to cause any significant adverse reactions in the body as a result of contact with bodily fluids or tissue, such as tissue death, tumor formation, allergic reaction, foreign body reaction (rejection), inflammatory reaction, or blood clotting. Moreover, biocompatibility means the material must not be susceptible to damage from long-term placement in the body.
The material of choice for conductive elements in implantable medical devices is platinum, following extensive trials performed over the years.
Given the above requirements, the manufacturing of wiring and connector components for implantable medical devices has developed into a labor intensive and highly specialized craft.
One particular area where this is evident is in the field of cochlear implants, which have been developed to provide the sensation of hearing to hearing impaired individuals.
A cochlear implant system bypass the hair cells in the cochlea to directly deliver electrical stimulation to the auditory nerve fibers, thereby allowing the brain to perceive a hearing sensation resembling the natural hearing sensation normally delivered to the auditory nerve. U.S. Pat. No. 4,532,930, the contents of which are incorporated herein by reference, describes one type of cochlear implant system.
The intracochlear electrode array has generally been manufactured by positioning a plurality of electrically conductive platinum rings (for example, 22) in a linear array, manually welding electrical conductive wires to each of the electrodes, and then molding a resiliently flexible carrier member about the array. Each of the wires is insulated from one another to minimize unwanted interaction between different electrical components.
In view of the high labor cost and complexity associated with the manufacturing of the conductive elements, a number of manufacturing alternatives have been investigated
For example, thin film technology can be used to create electrically conductive features on insulating surfaces on a micron scale. Such techniques include electroforming, vacuum deposition (sputtering, evaporation), and chemical vapor deposition.
However, the metallic films produced by these techniques can feature properties that are different from the corresponding properties of the original, bulk materials used. This results in the materials functioning differently from their intended purpose. Further, the integrity of the biocompatible material must be maintained, by avoiding or reducing any contamination introduced during the manufacturing process.
In the case of platinum, thin film techniques tend to result in cracking and delamination of the platinum. This forms a high impedance path which impairs the functionality of the device.
It is desirable to provide an improved method of manufacturing biocompatible conductive devices in the micron scale.